1. Field of the Invention
The present invention relates to an automatic tracking device for video cassette recorder (hereinafter referred to as VCR) designed to enable its reproduction head to achieve an accurate tracking on the tape track during reproduction and, in particular, to an automatic tracking device for VCR designed to achieve an automatic tracking by making compensation for driving phase of capstan motor according to the relative magnitudes of real color signal and cross talk signal among reproduced video signals.
2. Description of the Prior Art
In the VCR, generally, tracking condition of every tape must be adjusted to make compensation for interchangeability when it is recorded. In the prior art, however, the tracking condition of VCR is adjusted by the manual operation of tracking adjuster of variable resistance installed on the outside thereof.
Accordingly, the prior art is defective not only because tracking must be manually adjusted by the user every time a tape is used and it is difficult to achieve an accurate tracking adjustment by the manual operation of adjuster but also because once tracking is adjusted, the adjusted condition is kept until it is manually adjusted again and so tracking is not achieved in the best condition when a tape is reproduced for many hours.
Recently, there is a device which finds the mean value of detected signal by continuously detecting the envelope of video signal outputted from the reproduction head at a regular period and adjusts tracking automatically according to the differences between two signal values by comparing the mean value with the signal value of envelope detected at a regular period.
However, such a conventional device involves an error in basic concept itself where tracking is automatically controlled in the fixed basic value, since the envelope of video signal outputted from reproduction head according to the brightness of picture, the running condition of tape and the essential property which a tape possesses undergoes a change occasionally. It also requires an addition of new part in order to cope with a change in envelope by sampling and holding the detected signal value of envelope during both vertical and horizontal synchronization, but it still poses a problem caused by the abnormality of travel system or the irregularity of tape condition.
Furthermore, it must be provided with an exclusively-used microcomputer because, in the microcomputer, it requires to calculate the detected signal of envelope continuously and, at the same time, to achieve an automatic tracking by drawing a comparison between the mean value of the detected signal of envelope and the detected signal value of envelope at a regular period.